Motor vehicle drive shafts must be manufactured to close runout tolerances, particularly to avoid vibration and associated component drainage. Runout can result from a bent shaft, referred to as centreline runout (lack of straightness), and/or out of roundness (ovality or lack of circularity) of the shaft cross-section. Whilst a bent shaft can cause vibration, an out of round shaft will not. Excessive out of round will, however, weaken the shaft.
Drive shafts are typically inspected for runout by way of dial gauges or electro-optical measurement systems, measuring total runout of the drive shaft at various transverse cross-sections.
Whilst run out can be caused by either out of roundness or lack of shaft straightness, the current methods are unable to readily distinguish between these two causes or components of run out. The cause of run out is significant as run out caused by lack of shaft straightness can typically be readily rectified by way of a straightening press whereas out of round defects are typically not rectifiable and require rejection of the drive shaft.